Foreign matters if present on the wave propagation surface of a surface acoustic wave device undoubtedly influence the wave propagation and damage the expected characteristic of the device. To avoid this, the greatest attention has to be paid to protection of the wave propagation surface against contamination in its manufacturing process. In this connection, the prior art technology employs a hermetic seal using a metal or ceramic cavity member to provide a space-keeping covering of the wave propagation surface of a surface acoustic wave device.
FIG. 4 is a cross-sectional view of one form of the prior art hermetic can package in which a chip 1 is bonded to one surface of a stem 4 by an adhesive 6, and is connected to terminal pins 5 by bonding wires 3. The surface of the stem 4 including the chip 1, bonding wires 3 and terminal pins 5 is covered by a cap 2 which defines a sealed interior space above the upper surface of the chip 1.
The prior art sealing method, however, is somewhat expensive. Therefore, there is a great demand for an inexpensive, mass-productive sealing method in particular for surface acoustic wave devices for civilian-use equipments.